This invention relates to novel crystalline borosilicates, their method of preparation, and their use. More particularly, this invention relates to metal-cation-deficient crystalline borosilicate molecular sieve materials having catalytic properties and to various uses of such crystalline borosilicates.
Both natural and synthetic zeolitic materials have been known to have catalytic capabilities for many hydrocarbon conversion processes. Such zeolitic materials, often referred to as molecular sieves, are ordered porous crystalline aluminosilicates having a definite structure with large and small cavities interconnected by channels. The cavities and channels that are present throughout the crystalline material are generally uniform in size and permit selective separation of hydrocarbons. Consequently, these materials in many instances have come to be classified in the art as molecular sieves and are utilized for certain catalytic properties, as well as for selective adsorptive properties. The catalytic properties of these zeolitic materials are affected also, at least to some extent, by the size of the molecules that are allowed to penetrate selectively the crystal structure. Presumably, these molecules which penetrate the crystal structure of the crystalline molecular sieve material are contacted with active catalytic sites within the ordered structure of the material.
Generally, the term "molecular sieve" includes a wide variety of positive-ion-containing crystalline materials, which may be either natural or synthetic. They are generally characterized as crystalline aluminosilicate material, although other crystalline materials may be included in the broad definition. The crystalline aluminosilicates are made up of networks of tetrahedra of SiO.sub.4 and AlO.sub.4 moieties in which the silicon and aluminum atoms are cross-linked by the sharing of oxygen atoms. The electrovalences of the AlO.sub.4 tetrahedra are balanced by the use of positive ions, for example, alkali-metal cations or alkaline-earth-metal cations.
Many synthetic crystalline materials have been developed. Crystalline aluminosilicates are among such crystalline materials and, as described in the patent literature and the published journals, are designated by letters or other convenient symbols. Typical examples of such crystalline aluminosilicates are Zeolite A (U.S. Pat. No. 2,882,243), Zeolite X (U.S. Pat. No. 2,882,244), Zeolite Y (U.S. Pat. No. 3,130,007), Zeolite ZSM-5 (U.S. Pat. No. 3,702,886), Zeolite ZSM-11 (U.S. Pat. No. 3,709,979), Zeolite ZSM-12 (U.S. Pat. No. 3,832,449), and others.
U.S. Pat. No. 3,702,886, which discloses Zeolite ZSM-5 and its method of preparation, teaches the production of a zeolite wherein aluminum or gallium oxides are present in the crystalline structure, along with silicon or germanium oxides. The latter and the former are reacted in a specific ratio to produce a class of zeolites designated ZSM-5, which is limited to crystalline alumino- or gallo-silicates or germanates and which has a specified X-ray diffraction pattern. The above ZSM-11 and ZSM-12 patents are similarly limited to crystalline alumino- or gallo-silicates or germinates, also having specified X-ray diffraction patterns.
Manufacture of the ZSM materials utilizes a mixed base system in which sodium aluminate and silicon-containing material are mixed together with sodium hydroxide and an organic base, such as tetrapropylammonium hydroxide or tetrapropylammonium bromide, under specified reaction conditions, to form the desired crystalline aluminosilicate.
U.S. Pat. No. 3,941,871 claims and teaches an organosilicate having very little aluminum in its crystalline structure and possessing an X-ray diffraction pattern similar to the ZSM-5 composition.
Recently, as disclosed in a co-pending United States patent application, Ser. No. 897,360, filed in the United States Patent and Trademark Office on Apr. 18, 1978, there has been found a novel family of stable synthetic crystalline materials characterized as borosilicates, which are identified as AMS-1B and which have a specified X-ray diffraction pattern. Such crystalline borosilicates are formed by reacting a boron oxide and a silicon-containing material in a basic medium in the presence of an alkali metal or an alkaline earth metal.
U.S. Pat. No. 3,328,119 is directed to a synthetic crystalline aluminosilicate containing a minor amount of boria as an integral part of its crystal framework. This crystalline material is a boron-containing aluminosilicate and is not a crystalline borosilicate.
U.S. Pat. Nos. 3,329,480 and 3,329,481 relate to "zircono-silicates" and "titano-silicates", respectively.
U.S. Pat. Nos. 4,029,716; 4,049,573; 4,067,920; 4,078,009; and 4,086,287 relate to crystalline aluminosilicate zeolites having a silica-to-alumina ratio of at least about 12 and a constraint index within the approximate range of 1 to 12, and having combined therewith boron in an amount of at least about 0.2 weight percent as a result of reaction of the zeolite with a boron-containing compound. This is a crystalline aluminosilicate containing some boron and is not a crystalline borosilicate.
There has also been disclosed in the prior art the preparation of high-purity crystalline aluminosilicates, which aluminosilicates are prepared by the use of alkylammonium hydroxides or ammonium hydroxides. Such synthesized nitrogenous crystalline aluminosilicates are metal-cation deficient. "Hydrothermal Chemistry of the Silicates. Part IX. Nitrogenous Aluminosilicates." R. M. Barrer and P. J. Denny, J. CHEM. SOC., 971 (1961); and "Synthesis and Crystal Structure of Tetramethylammonium Gismondine", C. Baerlocher and W. M. Meier, HELVETICA CHIMICA ACTA, 53, 1285 (1970). Such disclosures do not consider crystalline borosilicates.
There has now been derived crystalline borosilicate material that is deficient in metal cations, that is, it is substantially free of metal cations.